New World Screwworm

Once eradicated from the US in the 1960s, New World screwworm is again driving prevention efforts as cases move closer to the US-Mexico border.

In September 2025, the FDA issued a conditional approval for another drug indicated to prevent and treat New World screwworm (NWS) larval infestations in cattle.

Although the parasite has not yet been detected in the US, officials warn that its northward movement poses a serious risk to livestock and wildlife.

Credelio Quattro (Elanco) was previously approved by the FDA for treatment of infestation for 6 other parasites in dogs.

The product is also indicated treatment and control of cattle fever tick.

A concise Q&A for veterinarians summarizing the identification, reporting, treatment, prevention, and practical next steps as the New World screwworm approaches the US border.

The FDA determined that Credelio Cat may be effective in treating New World screwworm infestations in cats and kittens.

The program is used to combat New World screwworm, a global health threat.

The authorization is the first of its kind for dogs, as health officials track New World screwworm cases near the US-Mexico border.

Most adult screwworms travel less than 10 miles to find a host. The greater risk comes from the movement of cattle, deer, and other hosts, explained Christopher Lee, DVM, MPH, DACVPM, in this Vet Watch update.

Zoetis' Dectomax-CA1 is the first drug to receive conditional approval in the US for addressing this type of parasitic infestation.

The case is the closest the parasite has come to the US during the current outbreak.

The first human case detected in US, plus a summary of how the US is responding to New World screwworm.

The declaration allows emergency use of animal drugs not yet FDA approved for screwworm treatment.

In this Vet Watch Update, our host Dr Christopher Lee shares more on what exactly normalcy bias means, and what it means for potential New World screwworm patients.

Have a suspected myiasis case? Christopher Lee, DVM, MPH, DACVPM, explains what to do, in this Vet Watch update.

Christopher Lee, DVM, MPH, DACVPM, provides his insights into the fight against New World screwworm—which includes an expanded screwworm production facility—in this Vet Watch update

The latest updates relating to animal care establishments and platforms.

This halt in imports is due to the rapid spread of the New World screwworm in Mexico, taking effect immediately.

Amid a surge to more than 1400 confirmed New World screwworm cases in Mexico and an immediate US suspension of live cattle imports, Christopher Lee, DVM, MPH, DACVPM, warns this parasitic fly could breach the southern border by year’s end, posing serious risks to livestock, pets, wildlife, and even human health.

The agreement also ensures ports remain open to livestock imports

USDA APHIS and Mexico are collaborating on New World screwworm screening and treatment measures

With screwworms advancing northward into Mexico, veterinarians must prepare for the possibility of widespread infestations

Veterinarians in the United States are asked to be on the lookout for signs of possible infections

The announcement comes after a diagnosis of New World screwworm in a horse